/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlineChatInterface.h
Kick off request for sending a chat message privately between users
if successfully started the async operation
bool SendPrivateChat ( const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & UserId, const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & RecipientId, const [FString](API\Runtime\Core\Containers\FString) & MsgBody )